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New Model Predicts How Debris-Covered Glaciers Will React to Climate Change

Glaciers are vulnerable to melting due to climate change, however debris-covered glaciers respond differently to changes in temperature due to insulation from the debris. A new model factors in this variable for debris-covered glaciers in order to predict how these glaciers will react to a changing climate. Focusing on the Khumbu Glacier in the Himalayas of Nepal, the model predicts a loss of 8-10% of total glacial mass by 2100 followed by increased losses as the tongue (frontmost part of the glacier where debris accumulates) separates from the rest of the glacier. This separation process exposes more surface area of the glacier which causes accelerated loss of mass.

Debris-covered glaciers typically lose less area than clean-ice glaciers, which conceals the magnitude of total mass of ice that is lost, although response time to warming is still greater than clean-ice glaciers. The debris at the tongue of the glacier insulates the tongue, slowing melting, but above the tongue, less or no debris causes melting in situ, causing the surface to lower, eventually separating the tongue from the rest of the glacier.

The new model has aligned with the behavior of the Kumbu Glacier since the end of the Little Ice Age and has been used to predict how this glacier will react to further climate change in the next 200 years given high and low warming scenarios by the IPCC report. The predictions of an 8-10% loss of total glacial mass by 2100 will be important for further modeling how the Himalayas and other mountain ranges will respond to climate change in the coming years.

Release of Carbon from Glaciers and Ice Sheets Increases with Further Melting

by Lindsay McCord

For the first time, researchers have estimated the total amount of dissolved organic carbon held in glaciers around the world — six petagrams. Climate change has further increased melting of glaciers, releasing organic carbon into downstream ecosystems. Organic carbon from glacial melt provides an important source of carbon to downstream ecosystems, but is increasing, and an estimated 15 teragrams of additional dissolved carbon is predicted to enter streams from glaciers by 2050 due to climate change. This has the potential to alter the carbon cycle of downstream ecosystems. Much of the organic carbon will be released into the atmosphere as CO2 by microbes, increasing greenhouse warming. Additionally, organic carbon could alter the biogeochemical balance in some proglacial ecosystems, especially downstream of mountain glaciers, as high-alpine valleys can have little soil and vegetation to uptake the carbon.

Hood et al. (2015) combined measurements from the Greenland Ice Sheet, the Antarctic Ice Sheet, and mountain glaciers to estimate the total amount of carbon stored in the terrestrial ice reservoir. Stable glaciers and ice sheets lose organic carbon yearly in cycles called annual mass turnover, but is regained through accumulation on the glacier surface, representing a net zero loss. However, when glaciers experience cumulative annual mass losses they become a source of additional fluxes of organic carbon to downstream ecosystems. Annual mass loss is associated with warming temperatures. Mountain glaciers are most vulnerable to annual mass loss and thus represent the largest source of glacial loss of organic carbon.